a long time ago; long before
Used to refer to something that happened far in the past, often with a sense of temporal distance from the present.
ずっと前にその映画を見た。
I saw that movie a long time ago.
彼は、ずっと前に引っ越してしまった。
He moved away a long time ago.
A fixed phrase composed of ずっと (continuously, much) + 前 (before) + に (particle). The combination is lexicalized as an adverbial expression meaning 'a long time ago'.